Powder image forming device



April 12, 1966 c. o. CHILDREss ETAL POWDER IMAGE FORMING DEVICE 3 Sheets-Sheet 1 Filed April 15, 1963 April 12, 1966 c. o. cl-uLDRl-:ss ETAL 3,245,341

POWDER IMAGE FORMING DEVICE Filed April 1s, 196s s sheets-sheet 2 April 12, 1966 c. o. CHILDREss ETAL' 3,245,341

POWDER IMAGE FORMING DEVICE Filed April 15, 1965 5 Sheets-Sheet 3 minimi United States Patent O 3,245,341 PWDER IMAGE FORMING DEVICE Clyde 0. Childress, Palo Alto, and Alonzo W. Noon,

Los Altos, Calif., assignors to Electrostatic Printing Corporation of America, San Francisco, Calif., a corporation of California Filed Apr. 15, 1963, Ser. No. 273,169 12 Claims. (Cl. lOl-122) This invention relates to devices for forming powder images which are then transferred to an image receiving medium for fixing thereon, Vand more particularly to improvements therein.

A number of different mechanisms have been employed in the field of electrostatic printing for forming a powder image which may then be transferred to an image receiving medium to be Xed thereon. One method is to form a charge image on a suitable medium and to then dust this medium with electroscopic powder particles which adhere to the charged portion of the medium. Thereafter, a receiving medium is brought into contact with the powder particles which are then attracted to the receiving medium by using a charge of suitable polarity to attract the powder particles onto the image receiving medium. Another arrangement comprises using an apertured screen having the apertures in the pattern of the image. Electroscopic particles are forced through the apertures of the screen into an electric eld which is established between the screen and an opposite member which may be the image receiving member. The electric eld operates to transport the electrosco-pic powder particles across to the image receiving member from the screen.

While the foregoing arrangements operate satisfactorily, they either require expensive materials or require considerable care and expense in their preparation to provide a desired image. Furthermore, there are practical limitations -on the depth of the layer of material which may be deposited, as well as on the materials which can be used when a screen is used as the image forming device.

An object of the present invention is to provide a powder image forming device which is simple and inexpensive to manufacture.

Yet another object of the present invention is to provide a novel image forming device.

Still another object of the present invention is to provide an image forming device wherein the depth of the powder image may be more precisely controlled than heretofore.

Yet another object of the present invention is the provision of 4a powder image forming device wherein the loading of powder for forming the image is effectuated more simply than has been possible heretofore.

Another object of this invention is the provision of a powder image forming device with which a much greater depth of material can be deposited on the image receiving device than heretofore.

Yet another object of this invention is the provision of a powder image forming device which enables the use of a greater variety of materials than was useable with prior electrostatic printing systems.

These and other objects of the invention are achieved by constructing a powder image forming device of a base material which is porous. This base material has openings therethrough which are large enough to allow the passage of air but which do not allow the passage of the powder particles which are used for printing. The material is given -an image forming surface by blinding or closing oit the air passages in the non-printing areas. This may be done by adhering a suitable apertured masking material to this surface or may be done by photo- 3,245,341 Patented Apr. 12, 1966 ice graphic means whereby the image printing pattern is developed photographically. The blinded or closed p0rtions of the surface may stand in relief from the surface which is not blinded, or may lie in substantially the same plane depending to some extent on the procedures which are employed in making the mask or the porous material. Thereafter, the porous material is passed through a powder cloud wherein the powder comprises electroscopic powder particles or may be actually dipped into a powder mass. A vacuum is applied to the back surface of the porous material during this time. As a result, powder particles adhere to the regions which do not have the openings blocked. Thereby, a powder image is provided on the surface. The mask may be retained in place during transfer of the image to an image receiving material or may be removed prior to the occurrence of such transfer. In either event, the powder image remains in place on the surface of the porous material until a transfer to the image receiving material occurs.

It is interesting to note the behavior of the powder particles under the binding influence of the negative air pressure. It behaves and feels as a putty-like mass, since it is completely captive to the surface, being planable and retaining an impression such as a fingerprint when made therein, and may also be precisely cut.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings, in which:

FIGURE l is an isometric view of an embodiment of the invention.

FIGURE 2 is a fragmentary view or section of FIG- URE l.

FIGURE 3 shows how the embodiment of the invention may be employed for continuous image forming and image transfer.

FIGURE 4 is a detail of the powder image forming drum shown in FIGURE 3.

FIGURE 5 is a view illustrating how the embodiment of the invention may be employed for continuously changing the powder image thereon.

FIGURE 6 is a fragmentary view of the arrangement shown in FIGURE 5.

FIGURE 7 is an illustration of how the embodiment of the invention may be employed with successive powder image forming masks being moved into printing position, and

FIGURE 8 shows an arrangement of the embodiment being used with continuous line printing.

FIGURE 9 illustrates the embodiment of the invention being employed without a mask being interposed between it and the image receiving material, and

FIGURE l0 illustrates the embodiment of the invention being employed fo-r multicolor image forming and transfer.

FIGURE ll illustrates van embodiment of the invention being used to transfer an image without an electric field.

FIGURE l2 illustrates an embodiment of the invention used as a coating device.

Reference is now made to FIGURES 1 and 2 which illustrate an embodiment of this invention. This comprises a porous base material 10, which has a plurality of openings 12, which extend therethrough. These openings are made smaller than the particles of powder or other material which are to be used with this powder image forming device. The term powder is meant to include materials having a particle size which is too large to clog the openings of the porous base material, but which is not so large that it cannot be handle-d by the porous base material in the manner to be described herein. Illustrative of the powder particle size, in an embodiment of the invention which was built, the porous opening size at the outer periphery of the porous base material was on the order of 2 mils and the powder particle size ranged from 2 mils up to approximately 30 mils with the average size being on the order of mils.

The porous material may be sintered bronze spheres or particles, or fibrous steel, which materials are conductive, or ceramic or fibre, or plastic, which if desired, may be treated so as to be conductive. These materials have openings which allow the passage of air therethrough. One side of the base materials 10 is given an image bearing surface by applying a mask 14, which closes off air passages to the non-printing areas.

The mask 14, has openings 16 therein, which provide a pattern for the desired image for the powder. The mask may comprise simple materials such as non-previous paper tape which has openings cut or stamped in it, with the desired pattern. The mask may be made photographically by adhering a photosensitive gelatin emulsion or a photo-polymer that when exposed to a light image is differentially hardened in response thereto. This coating may be developed by washing away the unhardened portions. Alternatively, the coating may be made by using the photo sensitive gelatin which is placed on a temporary substrate, developed there, and then adhered to the porous material and the substrate removed. Obviously, any screen with all apertures masked except those which are arranged in the desired image pattern may be adhered t0 a surface of the porous material to provide a powder image forming device. The blinded or closed portions of the device may stand in relief from the surface of the porous plate as is shown or may lie substantially in the same plane depending upon the procedures used in forming the mask. For example, an image may be printed on the surface of the porous material with .an ink comprising a liquid which hardens and masks off, wherever it is deposited the porous openings in the porous material.

The foregoing methods and procedures for masking off all but desired areas of the porous material surface are given by way of example, `and are not to be construed as a limitation upon the invention.

To use the embodiment of the invention shown in FIGURE l, a negative air pressure or vacuum is applied to the unmasked side of the porous material. The masked side is then either brought in contact with a mass of the powder particles which are to be used, or is inserted in la cloud of these powder particles. Because of the negative air pressure the powder particles are drawn onto the exposed surface of the porous material and thereby assume the pattern of the image desired. The excess powder which may adhere to the masked portion of the surface may be easily blown away, or brushed away, or scraped off by a doctor blade. Then when it is desired to transfer the powder image the negative air pressure is removed from the unmasked surface of the porous material and the image receiving surface may either be brought directly in contact with the masked surface, or may be spaced therefrom by a suitable distance. An electric field with a suitable polarity may be established for transferring the power particles which, for this kind of transfer, preferably have electroscopic properties, to the image receiving surface. During the course of the transfer, there may be relative motion between the image receiving element and the powder image forming surface. That is, either the powder image forming surface may be rolled over the image receiving surface or vice versa, or both image forming surface and the powder image receiving surface may be rotated in opposite directions and the transfer of the powder image is still effectuated, so long as the surface speeds are synchronized in the transfer area.

With certain powders, the transferring force of the electric field may be such as to exceed the vacuum restraining force whereby the vacuum need not be turned off at the time of transfer.

As will be shown subsequently herein, the electrostatic field can be omitted and `a transfer may also be made from the image forming device to an image receiving surface either by making the image surface tacky, so that the powder particles on the image forming device will adhere to the tacky surface when it is brought in contact with the image forming device surface, or another vacuum can be applied to the rear surface of a porous image receiving surface which causes a powder image transfer to occur' when the front surface is brought in contact with thc surface of the image forming device.

FIGURE 3 is a perspective View showing how the powder image transfer device may he employed for printing on a movable image receiving web, and FIGURE 4 shows details of the transfer device. The porous base material is shown in the form of a rotatable cylinder 20 which is conductive and which has a hollow center 22, Iwhich is capped at both ends by end plates 21A and 21B. The cylinder is rotatably mounted on a hollow shaft 23 on which it can rotate. A negative air pressure is applied from a vacuum source 24, through a pipe 26 and through openings in the hollow shaft 23, to all of the center 22, of the cylinder cavIty, except for a V-shaped region defined by two stationary walls 2S, 30, represented by the dotted lines in FIGURE 3. These walls are fixedly supported on the shaft 23 within the hollow center to prevent the negative air pressure from being applied to an arcuate portion of the cylinder 2t) enclosed therebetween. The ends of the walls 28, 30, which brush against the inner wall of the porous cylinder, may be lined with felt or rubber so that they will rub against the inner surface, blocking off the negative air pressure while permitting the cylinder to be rotated. The cylinder is rotatably driven from a motor 31.

The cylinder 2i) has an apertured mask surface 32, of the type previously described. As the cylinder rotates it carries the masked surface 32 into a powder loading container 34. This container will hold a charge of electroscopic powder particles which are drawn to the open areas of the porous cylinder surface as defined by the mask thereon. The powder particles may be directed toward the surface by any suitable type of feeder, or may be applied in the form of a powder cloud. This is formed by providing the base of the container 34, with an apertured plate through which air under slight pressure is fed from a positive air pressure source 35. This causes the powder in the container to form a cloud. As the cylindrical surface passes through a cloud, powder particles are drawn down on the exposed areas of the porous cylinder.

The trailing end of the container 34 has a doctor blade 36, thereon, for the purpose of removing any excess powder from regions other than the aperturcd portions of the mask. As the cylinder continues to rotate, the powder particles are adhered to the regions of the cylinder to which they are drawn. A web 38, which constitutes the image receiving surface, is fed, at a matching speed with the speed of rotation of the cylinder, over a portion of the surface thereof. The region over which the web 38 passes over the surface of the cylinder encompasses the region of the cylinder to which no negative air pressure is applied. Accordingly, the powder image can be transferred to the image receiving web during the interval that the cylinder traverses the non-negative air pressure region.

A preferred way of transferring this powder is to em ploy an electric field. This is established, where the 4web 38 itself is not sufficiently conductive, by connecting a source of field establishing potential 46, between the conductive plate 44, and the conductive porous material of which the cylinder 20 is formed. A roller electrode 48, may be employed for contacting the porous material. This roller electrode is connected through a switch 50 to the source of field establishing potential 46. The web 38, after passing over the surface of the cylinder 20, is then carried to a powder image fixing station, not shown.

It can happen that the ends of the walls 28, 30, which rub against the inner side of the cylinder 20, do not provide a good enough vacuum seal through poor fitting or wear. In such a case, as shown in FIGURE 4, if the transfer force of the electric eld is not strong enough a slight positive pressure of air may be fed to the V-shaped region from a positive pressure source 39, through a pipe 41, which connects to suitably placed openings in the pipe 23.

The arrangement shown in FIGURE 3 is employed where the mask is Iwrapped around the surface of the cylinder. If desired, the mask may be made removable and is removed when it is desired to change the pattern which is being printed, to be replaced by another mask. In FIGURE 5, there is shown an arrangement for using a movable mask where it is desired to continuously change the printing pattern, for example, to print a magazine or a book. A porous cylinder 60, is shown in FIGURE 5, which has the identical construction as the porous cylinder in FIGURE 3. The center is hollow and negative air pressure is fed therein to all but a V-shaped region 62, which is blocked off by walls 64, 66, from the remaining portion of the center of the cylinder. As previously described, a positive air pressure may be fed into this V-Shaped region if required.

A powder feeding container 68, is positioned so that the rotatable cylinder 61), in rotating, passes its surface therethrough. The electroscopic powder particles are directed onto the surface of the cylinder by any suitable means such as the powder cloud mentioned previously. These powder particles adhere to the -cylindrical surface by reason of the negative pressure applied to the openings extending through the cylinder from the center. A doctor blade 70, provides a proper powder thickness on the surface of this cylin-der by scraping off any excess powder beyond the predetermined thickness.

An apertured mask 72, in the form of a web, is fed from a feed roller 80, over the surface of the cylinder 613, to which it is tightly adhered by means of guide rollers respectively 82, 84, positioned below the top of the cylinder 60, and then to a take-up reel, 86. An image receiving web 88, is fed in proximity to the surface of the mask 72, by means of two guide rollers 91), 92. The image receiving web 88, preferably is made to conform to the circular surface of the mask when it is spaced from the mask by guides at the edges, not shown or may be brought in contact with the mask by suitably depressing the rollers 96, 92, suiiiciently to have the image receiving material 88 ride over the surface of the mask.

It will be noted that the sector of the arc to which no negative air pressure is applied is encompassed within the region of the surface of the cylinder over which both the mask 72 and the image receiving web 88 pass. It should also be noted that the speeds of travel of the cylinder 60, the mask 72, and the web 88, are all adjusted so that they are moving at the same speed during contact or when they are in proximity with one another. A conductive back :plate 94, which is employed when the image receiving material 88 is not ,sufficiently conductive for etfectuating an electrostatic transfer, is posi- 'tioned over the desired image transfer region which is the sector subtended by the V-shaped region 62. An electric field establishing potential 96, is connected between the back plate and through a switch 98 and a contacting brush 100, to the conductive porous cylinder. As a result, the electroscopic powder particles are transferred to the image receiving member 88, only from those areas of the surface of the porous cylinder which are not masked off by the mask 72. As the cylinder continues to rotate, its surface moves out from under the mask and then down into the container 68, where powder on the surface is renewed.

Any suitable mechanism for causing the image receiving element to acquire a charge opposite to that of the electroscopic powder, such as a corona discharge device behind the element to establish a field and charge the element may be used in place of the backing fplate.

FIGURE 6 shows the appearance of a portion of the cylindrical surface 60 with the mask 72 thereon. The mask may be of the stencil screen type. The apertures 73, in the mask, expose the powder particles 75, which have been adhered to the surface by the negative air pressure. It is the powder particles in these regions which are formed in the shape of the image which is transferred across to the receiving web.

FIGURE 7 is a View in elevation illustrating how discrete powder image forming devices may be employed for transferring an image to, for example, containers 162, 104, 106, which are carried on a conveyor belt 108. There is shown, by way of example, six discrete powder image forming devices 110, 112, 114, 116, 118, and 120. Each one of these constitutes a porous plate having an apertured mask adhering to the surface thereof. The back of each one of these porous plates is covered by an enclosed housing member respectively 122, 124, 126, 128, 130, 132. Each one of these members is connected to a rotating head 134, which supplies neg-ative air pressure to the back sides of all of the porous plates except to the one 120, which is in the printing position. An electroscopic powder loading container 136, is placed in the path that each one of these powder image fixing devices takes in passing from the image transfer location, and then around to receive another charge of powder and then back to the image transfer location.

The rotatable support 138, for the powder image tixing plates may be any suitable type of mechanism, such 'as a belt, with suitably shaped apertures cut therethrough into which these devices may be inserted or may be properly spaced and rotatably mounted belts or chains between which these plates are supported. The rotatable vacuum supplying head 134, can comprise a vacuum feed device which includes a valving which is cam operated so that when a member reaches the printing position the vacuum is cut off therefrom.

As the various powder image forming plates are transported they pass through the powder loading container 136, where, because of the vacuum applied to the porous back surface of the plate 118, powder is caused to adhere to those areas of the surface which the mask thereon permits to become exposed. The plates are then carried around until they meet one of the containers 104.

When one of the loaded image forming plates reaches the printing position, which is the one in which the plate is shown in FIGURE 6, the containers which are spaced along the -conveyor belt to meet a plate at the printing position will contact it and for a short time the two can travel together while the powder image is being transferred from the image forming plate to the container 104. An electric field is established at this time by connecting a eld establishing .potential source 140, either to the container, if it is conductive, or to the belt on which the container rides, to make contact with the container in this manner. The image forming plate is grounded through a roller electrode 142, when it reaches the printing position and thereby is connected to the field establishing potential source 140.

The arrangement shown in FIGURE 7 for transferring an image uses separate powder image transfer plates. A drum, of the type shown in FIGURE 3, may be employed to transfer the image. This is shown in FIG- URE 8. A drum 144, which is identically constructed with the one described in connection with FIGURE 3, has the V-shaped region 146, therein, to which there is no negative air pressure applied, located at the position at which a rolling contact will be made with an image receiving object 148, carried thereby on a conveyor belt 150. The drum 144, rotates through a powder loading l container 152, which applies powder to the regions of the surface of the porous drums which are exposed by reason of apertures in the mask 154, which is on the surface of the drum. A doctor blade 156, cleans the excess powder from the surface of the drum. The image receiving object 14S, is carried past the periphery of the drum 144, which effectively rolls the surface thereof in contact with the surface of the object 148. A field establishing potential source 158 is `connected to the object 148, and through a roller electrode 160, to the conductive porous material. This establishes the electric field whereby the transfer of the powder image across to the surface of the image receiving element 14S is effectuated. Fixing of the powder image occurs after it passes the drum, in accordance with any of the methods known to this art. As the drum 144 rotates, it picks up a fresh powder charge in the image forming regions of the periphery and thereby transfers this powder image to the next object passing on the conveyor belt 150.

FIGURE 9 shows an arrangement of the embodiment of the invention wherein the mask is removed from the powder image forming device before the image transfer occurs. The image device is a drum 162, made of porous material of the type described. A mask 164, having image apertures therein, and which is in the form of an endless web, is carried by three rollers respectively 166, 16S, 170, in a manner to cover a portion of the surface of the drum 162 just before, during and after, its passage through the powder loading container 172. Since a negative air pressure is applied from a vacuum source 174, to the center of the drum, powder will adhere to the regions of the drum surface which are exposed through the mask apertures to the powder in the loading container.

When the mask is moved away from the surface of the drum as both continue to move out of the powder loading container, the powder image on the surface of the container remains in place since the negative air pressure is applied thereto. A transfer of the powder image is made at an image transfer position to a container 176, shown by way of example, which is carried by a conveyor belt 178 past the drum periphery either in Contact therewith or spaced therefrom by a very small distance. The electric field potential source 180, is connected, by means of a switch 182, to a contact 184, which contacts a container as it passes through the image transfer position. The drum is connected to ground whereby an electric field may be established which can carry the powder image to the container.

If the container 176 has a tacky surface, it can be brought in contact with the powder image on the surface of the drum 162, to cause the powder image to adhere to said tacky surface either without using the electric field transfer mechanism, or using it to assist in the transfer if desired.

FIGURE shows an arrangement of the embodiment of the invention for effectuating a multicolor powder image and powder image transfer. The drum 180 is made of porous material and has a vacuum applied to its hollow center as previously described. Three apertured masks respectively 132, 184, 186, are spaced around the periphery of the drum and are respectively supported by sets of rollers respectively 182A, B, C, D, 184A, B, C, D, and 186A, B, C, D, to be carried into masking Contact with the surface of the drum 18) to cover said surface, except for the apertures, while said drum surface passes through the three different color powder charging containers 188, 190, 192.

The timing of the arrangement and the mask openings are made such that the drum will have on its surface a complete powder image as it passes out from under mask 186. Mask 182 provides apertures for the blue color portions of an image. Mask 184 provides apertures for the red portion of the image and mask 186 provides apertures for the green portion of an image. An image receiving web 194 is used this time, by way of example.

It contacts the drum surface or may be slightly spaced therefrom, over an image transfer region while an electric field is established between the web and drum by a potential source 196, connected between web and drum. It should be appreciated that FIGURE l0 shows an arrangement for powder image forming and transfer with three colors. This is shown by way of example and not as a limitation.

FIGURE 1l shows how the powder image device, in accordance with this invention, may be used to provide an image transfer without an electric field. Two porous material drums respectively 198, 200, are shown, both constructed in the manner previously described, to permit a negative air pressure to be applied from respective source 202, 204, to the respective drum interiors. No V-shaped atmospheric pressure regions at the image transfer region need be reserved for drum 19S. However, the negative air pressure is preferably applied only to a sector of drum 200 which defines the image transfer and fixing regions. Vacuum source 204, provides a greater negative air pressure than vacuum source 202.

There is an apertured mask 206, provided for the periphery of drum 198. Thus, a powder image is formed on the periphery of drum 198 as it passes through the powder charging container 208. The powder image is carried to the image transfer region where it is brought in Contact with an image receiving web 210. The web 210 is guided around the periphery of the drum 200 by rollers 212, and 214. The web is preferably made sufficiently porous to permit the negative air pressure to pull the powder image to the web where it adheres until fixed in passing by the fixing station 216. The fixing may be by heat or by vapor spray. The web moves out from under the fixing station and then away from the roller 200.

There has been described and shown herein a novel and useful powder image forming device whereby the image is easily established and the powder image forming device is quickly and simply loaded. The transfer of the image can occur most expeditiously since powder particles do not have to be pushed through an intervening screen or other device but are loaded on the image forming device on the side facing the image receiving element. It should further be noted that one may load the image forming device with powder particles which are level with the mask on the surface of the porous backing, or may extend this mask sufficiently so that the powder particles which are attracted to the porous openings in the exposed surface do not come to the level of the mask surface. In this manner the mask may serve as a spacing element between the conductive surface in which the powder particles are deposited and the image receiving member to provide an electrostatic transfer of the powder particles to the image receiving member. Further, this insures a uniform spacing. Alternatively, the mask may be made substantially iiush with the porous surface whereby the powder particles which are attracted to the surface of the porous body by virtue of the negative air pressure applied to the other side, stand above the surface of the powder image 'forming member. Here the doctor blade is not used for removing any excess powder. Air pressure may then he used. For certain types of printing for example, on hot objects, which might adversely effect the mask material, this may be desirable.

It is interesting to note that the powder particles, when attracted to the porous surface adhere to this surface even after the vacuum is removed. They also adhere to one another despite the deposition on the surface to a considerable depth. The reason `behind this is not clearly understood. it is believed to be either or both the triboelectric charge phenomenon as well as the fact that the powder particles are rather granular and adhere to one another `simply due to the compaction of the particles.

In the foregoing description the mask has been described as establishing the powder image by having apertures therein in the shape of the desired powder image. A negative powder image can also be formed =by having apertures -in the mask in `all locations except in regions which define a desired image. It is to be understood that this is within the spirit and scope of this invention and these claims.

As thus far described, this invention is used to deposit an image on an image receiving surface using a masking device of some type to define the image. It should be appreciated that the deposit of an image operates to coat the surface with the particles deposited over the region of the image. Printing and coating are analogous. Obviously, if it is desired to Vcoat a portion of a surface, this invention may be employed lfor such a purpose and the mask will only cover those regions of the porous surface which are not to be used, for coating. If a complete surface is to `be coated with powder particles, then the mask is omitted. The porous body without a mask, has a negative air pressure applied to one side and the other side is then passed through the powder box, as has lbeen previously described. Then a transfer of the particles from the surface of the porous body to the surface to be coated is made to take place using any of the techniques described herein for making the transfer, that is with an electric field or using a tacky surface or a vacuum.

FIGURE 12 illustrates the use of ya porous roller for coating an entire surface. A web 220 having a tacky surface is 'fed from a supply reel, not shown, and is mad-e to pass a porous roller 222, in a manner so that its tacky surface contacts the surface of the porous roller. The porous roller 222 may be constructed in a manner similar to one of th-ose shown previously herein. The web 220 is maintained pressed against the surface of the porous roller 222 by the two spaced idler rollers 226, 228. Negative air pressure from a vacuum source 230 is fed to the inner surface of the porous roller. The porous roller is rotated Iby any means, such as a motor, not shown. Its outer surface is made to pass through a powder Ibox 232, where its -outer surface loads up with a covering of powder particles. A doctor blade not shown, mounted at the exit side of the powder box may be used to determine the depth of the powder particle covering. The powder particle covering of the porous cylinder surface is thereafter transferred to the web tacky surface, where they contact, resulting in Iapplying a coating to the web surface.

There has accordingly been described and shown herein a novel, powder image forming device which has utility in forming and transferring powder images Ito a receiving element which may `cover ya part or all of said receiving element surface `as may be desired.

We claim:

1. A powder image printing system comprising a source of powder particles, a porous body having an outer surface, an inner surface opposite said outer surface and having its porous openings extending between said inner :and outer surfaces, the size of said porous openings at said outer surface being smaller than the size of the smallest of said powder particles, means for applying powder particles from said source to said porous body outer surface, means for applying negative air pressure to the inner surface of said lbody while said powder particles are being applied to cause said powder particles to ladhere to the outer surface of said porous body, a powder image trans-fer location, means for presenting the image receiving surface of an article having an image receiving surface to the powder image transfer location, means for moving said porous body to said powder image transfer location opposite said image receiving surface, means for -masking all of said outer surface of said porous body at said powder image transfer location except for areas of said outer surface which are in the shape of a desired image, means for preventing the application of negative Iair pressure to said porous body while at said powder image transfer location, and means at said powder image transfer location `for transferring the powder in said unmasked areas to the image receiving surface of the image receiving member.

2. A powder image printing system as recited in claim 1 wherein said means for masking all of said outer surface of said por-ous body is 'a conductive ima-ge screen, said powder particles are electroscopic, and said means for transferring the powder covering the areas in the shape of the desired image to said image receiving surface includes means including said conductive screen for establishing an electric field extending between said screen and said image receiving surface at said powder image transfer location.

3. A powder image printing system as recited in claim 1 wherein said porous lbody is conductive, said powder particles are electroscopic, `and said means for transferring the powder covering the are-as in the shape of the desired image to said image receiving surface includes means including said porous body for establishing an electric field extending between said porous body and said image receiving surface at said powder image transfer location.

4. A powder image printing system as recited in claim 3 wherein said porous body is cylindrical and said means for moving said porous body comprises means for rotating said cylindrical body.

5. A powder image printing system comprising a source of powder particles, a conductive porous body having an outer surface, an inner surface opposite said outer surface, and having its porous openings extending between said inner and outer surface, said porous openings being smaller at said outer surface than the size of the smallest of. said powder particles, means for applying a mask having desired image apertures therein to said outer surface of said porous body at a first location and thereafter removing said mask, means for applying powder particles from said source to said mask covered outer surface of said porous body at said first location, means for applying negative air pressure to the inner surface of said body while said powder particles are lbeing applied to cause said powder particles to adhere to said outer surface in the shape of the image apertures of said mask, a powder image transfer location, means for presenting the image receiving surface of an article having an image receiving surface to said powder image transfer location, means for moving said porous body to said powder image transfer location from said first location, means for discontinuing the application of negative air pressure to said porous body while at said powder image transfer location, and means for transferring said powder image from said porous body to said image receiving surface.

6. A powder image printing system as recited in claim 5 wherein said powder particles are electroscopic, and said means for transferring said powder image from said porous body to said image receiving surface includes means including said conductive porous body for establishing an electric field between said porous body and said image receiving surface to move said powder ima-ge to said image receiving surface.

7. A powder image printing system as recited in claim 6 wherein said conductive porous body is cylindrical and said means for moving said porous body comprises means for rotating said cylindrical body.

8. A powder image transfer system comprising a source of electroscopic powder particles, a cylinder of conductive porous material having a hollow center, said cylinder having an inner surface, an outer surface, and porous openings extending from said inner to said outer surface, the size of the openings at said outer surface being smaller than the size of the smallest of said powder particles, stationary means for applying a negative air pressure to said inner surface over a predetermined cylindrical arc, means for applying powder particles to a portion of said cylinder outer surface in the shape of a desired powder image from said source of powder particles while said inner surface portion is within said predetermined cylindrical arc, a powder image transfer location at a position outside of said predetermined cylindrical arc, means for rotating said porous cylinder for cyclically moving its outer surface in a path adjacent said means for applying powder particles and through said powder image transfer location, means for presenting the image receiving surface of an article having an image receiving surface to said powder image transfer location opposite said porous cylinder outer surface, and means including said conductive cylinder for establishing an electric field between said cylinder and said image receiving surface at said powder image transfer location for transferring said powder image thereto from said outer surface.

9. A powder image printing system comprising a source of powder particles, a porous body having an outer surface, an inner surface opposite said outer surface and having its porous openings extending between said inner and outer surface, the size of said porous openings at said outer surface being smaller than the size of the smallest of said powder particles, a mask covering the outer surface of said porous body, said mask having apertures therethrough which are in the shape of desired images, means for applying powder particles to the mask covered surface of said porous body from said source of powder particles, means for applying negative air pressure to the inner surface of said `body while said powder particles are being applied to cause said powder particles to adhere to the areas of said outer surface of said porous body, which are exposed through the apertures of said mask, a powder image transfer location, means for presenting the image receiving surface of an article having an image receiving surface to the powder image transfer location, means for moving said porous body to said powder image transfer location opposite said image receiving surface, means for preventing the application of negative air pressure to said porous body while at said powder image transfer location, and means for transferring the powder on the exposed areas of said porous body to said image receiving surface at said powder image transfer location.

10. A powder image printing system as recited in claim 12 9 wherein said means for masking all of said outer surface of said porous body is a conductive image screen, said powder particles are electroscopic, and said means for transferring the powder covering the areas in the shape of the desired image to said image receiving surface includes means including said conductive screen for establishing an electric field extending between said screen and said image receiving surface at said powder image transfer location.

11. A powder image printing system as recited in claim 9 wherein said porous body is conductive, said powder particles are electroscopic, and said means for transferring the powder covering the areas in the shape of the desired image to said image receiving surface includes means including said porous body for establishing an elec tric field extending between said porous body and said image receiving surface at said powder image transfer location.

12. A powder image printing system as recited in claim 11 wherein said porous body is cylindrical and said means for moving said porous body comprises means for rotating said cylindrical body.

References Cited by the Examiner UNITED STATES PATENTS 1,668,322 6/1928 Kessler l0ll 16 X 2,029,273 1/1936 Montgomery et al. 10l-12l X 2,419,695 4/1947 Shuttleworth etal. l0l--ll6 X 2,468,400 5/1949 Huebner lOl- 119 2,525,135 10/1950 Hu 210404 2,590,321 3/1952 Huebner.

2,787,556 4/1957 Haas ll7-17.5 2,788,860 4/1957 Turner 55-400 3,008,826 11/1961 Mott et al.

3,063,216 l1/1962 Silverman 55-351 3,129,442 4/1964 Leckie lOl- 129 ROBERT E. PULFREY, Primary Examiner.

WILLIAM B. PENN, DAVID KLEIN, Examiners.

PAUL R. WOODS, Assistant Examiner. 

9. A POWDER IMAGE PRINTING SYSTEM COMPRISING A SOURCE OF POWDER PARTICLES, A POROUS BODY HAVING AN OUTER SUR- 